1. Field of the Invention
The present invention relates generally to wireless communications and more particularly to antenna systems with polarization diversity.
2. Description of the Related Art
In communications systems, there is an ever-increasing demand for higher data throughput and a corresponding drive to reduce interference that can disrupt data communications. For example, in an Institute of Electrical and Electronics Engineers, Inc. (IEEE) 802.11 network, an access point such as a base station may communicate with one or more remote receiving nodes such as a network interface card over a wireless link. The wireless link may be susceptible to interference from other access points and stations (nodes), other radio transmitting devices, changes or disturbances in the wireless link environment between the access point and the remote receiving node and so forth. The interference may be such to degrade the wireless link by forcing communication at a lower data rate or may be sufficiently strong as to completely disrupt the wireless link.
One solution for reducing interference in the wireless link between the access point and the remote receiving node is to provide several omnidirectional antennas in a ‘diversity’ scheme. In such an implementation, a common configuration for the access point includes a data source coupled via a switching network to two or more physically separated omnidirectional antennas. The access point may select one of the omnidirectional antennas by which to maintain the wireless link. Because of the separation between the omnidirectional antennas, each antenna experiences a different signal environment and each antenna contributes a different interference level to the wireless link. The switching network couples the data source to whichever of the omnidirectional antennas experiences the least interference in the wireless link.
One problem with using two or more omnidirectional antennas for the access point is that typical omnidirectional antennas are vertically polarized. Vertically polarized radio frequency (RF) energy does not travel as efficiently as, for example, horizontally polarized RF energy inside an office or dwelling space. To date, prior art solutions for creating horizontally polarized RF antennas have not provided adequate RF performance to be commercially successful.